The 3GPP (3rd Generation Partnership Project), which is a standardization project for mobile communication system, has been developing the standardization of LTE Advanced, which is an advanced version of LTE (Long Term Evolution) after the 3GPP Release 10 (see, for example, 3GPP TS 36.300 v10.4.0).
In LTE-Advanced, discussion has been made on provision of a heterogeneous network in which a low-power base station (so-called, a pico cell base station or a home base station) is installed in a coverage area of a high-power base station (so-called, a macro base station). The heterogeneous network can distribute a load of the high-power base station to the low-power base station.
In addition, with a view to both providing backward compatibility with LTE and achieving a wider bandwidth, a carrier aggregation technique is introduced to LTE Advanced, in which a carrier in LTE is used as a component carrier (CC) and multiple carriers are used in combination for radio communications. Note that a “carrier” is sometimes treated as a “cell”.